以下查询需要大约10分钟到1小时才能执行。由于这个原因，我们经常遇到负载峰值。任何人都可以帮助以更优化的方式重写查询。
查询：
select count(*)
from t_tab6 tab1
left join t_tab6_element_tab2 tab2
on tab2.tab6_id = tab1.id
left join t_tab3 tab3
on tab1.create_tab3_id = tab3.id
left join t_tab4 tab4
on tab2.element_id = tab4.id and tab2.element_type_id = 1
left join t_tab7 tab5
on tab2.element_id = tab5.id and tab2.element_type_id = 2
where tab1.domain_id = 522
解释计划：
+----+-------------+-----------+--------+-------------------------+-------------------------+---------+----------------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+--------+-------------------------+-------------------------+---------+----------------------------+--------+-------------+
| 1 | SIMPLE | tab1 | ref | domain_id_tab6_type_cd | domain_id_tab6_type_cd | 4 | const | 243430 | |
| 1 | SIMPLE | tab2 | ref | FK_tab6 | FK_tab6 | 4 | comp1.tab1.id | 2 | |
| 1 | SIMPLE | tab3 | eq_ref | PRIMARY | PRIMARY | 4 | comp1.tab1.create_tab3_id | 1 | Using index |
| 1 | SIMPLE | tab4 | ref | id | id | 4 | comp1.tab2.element_id | 1 | Using index |
| 1 | SIMPLE | tab5 | ref | id | id | 4 | comp1.tab2.element_id | 1 | Using index |
+----+-------------+-----------+--------+-------------------------+-------------------------+---------+----------------------------+--------+-------------+
5 rows in set (0.45 sec)
表格结构：
mysql> show create table t_tab6_element_tab2\G
*************************** 1. row ***************************
Table: t_tab6_element_tab2
Create Table: CREATE TABLE `t_tab6_element_tab2` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`element_type_id` int(11) NOT NULL,
`tab6_id` int(11) NOT NULL,
`element_id` int(11) NOT NULL,
`element_desc` varchar(500) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `FK_tab6` (`tab6_id`),
KEY `element_type_id_element_id` (`element_type_id`,`element_id`)
) ENGINE=InnoDB AUTO_INCREMENT=45901159 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> show create table t_tab3\G
*************************** 1. row ***************************
Table: t_tab3
Create Table: CREATE TABLE `t_tab3` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
`password` varchar(255) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
`is_admin` int(11) DEFAULT NULL,
`phone` varchar(50) DEFAULT NULL,
`company` varchar(255) DEFAULT NULL,
`last_login` datetime DEFAULT NULL,
`state` int(11) DEFAULT NULL,
`validate_code` varchar(50) DEFAULT NULL,
`has_login` smallint(6) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1304 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> show create table t_tab6\G
*************************** 1. row ***************************
Table: t_tab6
Create Table: CREATE TABLE `t_tab6` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`create_tab3_id` int(11) DEFAULT NULL,
`tab6_create_date` date DEFAULT NULL,
`tab6_type_cd` int(11) NOT NULL,
`tab6_desc` varchar(512) NOT NULL,
`IsGlobaltab6` int(2) DEFAULT NULL,
`tab6_start_date` datetime NOT NULL,
`tab6_end_date` datetime NOT NULL,
`job_id` int(11) DEFAULT NULL,
`domain_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `tab6_tab3_FK` (`create_tab3_id`),
KEY `domain_id_tab6_type_cd` (`domain_id`,`tab6_type_cd`)
) ENGINE=InnoDB AUTO_INCREMENT=8586007 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> show create table t_tab4\G
*************************** 1. row ***************************
Table: t_tab4
Create Table: CREATE TABLE `t_tab4` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`tab4_name` varchar(255) DEFAULT NULL,
`tab4_value` varchar(255) DEFAULT NULL,
`type` int(11) DEFAULT NULL,
`description` varchar(2000) DEFAULT NULL,
`own_domain_id` int(11) DEFAULT NULL,
`rank_check` int(11) DEFAULT NULL,
`rank1` int(11) DEFAULT NULL,
`rank2` int(11) DEFAULT NULL,
`rank3` int(11) DEFAULT NULL,
`yesterday_entrances` int(11) DEFAULT NULL,
`week_entrances` int(11) DEFAULT NULL,
`current_ctr` float(16,4) DEFAULT NULL,
`monthly_search_volume` int(11) DEFAULT NULL,
`avg_monthly_search_volume` int(11) DEFAULT NULL,
`traffic_increase` int(11) DEFAULT NULL,
`rank_improvement` int(11) DEFAULT NULL,
`rank_update_date` date DEFAULT NULL,
`top_rank_tab5_id` int(11) DEFAULT NULL,
`frequency` int(10) DEFAULT '1',
`score` float DEFAULT NULL,
`create_date` datetime DEFAULT NULL,
`bing_rank1` int(10) DEFAULT NULL,
`bing_rank2` int(10) DEFAULT NULL,
`yesterday_bing_entrances` int(11) DEFAULT NULL,
`bing_rank_improvement` int(11) DEFAULT NULL,
KEY `id` (`id`),
KEY `tab4_name` (`tab4_name`),
KEY `own_domain_id` (`own_domain_id`,`rank_check`),
KEY `rank_check` (`rank_check`)
) ENGINE=InnoDB AUTO_INCREMENT=670267018 DEFAULT CHARSET=utf8
/*!50100 PARTITION BY RANGE (`rank_check`)
(PARTITION p0 VALUES LESS THAN (0) ENGINE = InnoDB,
PARTITION p1 VALUES LESS THAN (1) ENGINE = InnoDB,
PARTITION p2 VALUES LESS THAN (2) ENGINE = InnoDB,
PARTITION pEOW VALUES LESS THAN MAXVALUE ENGINE = InnoDB) */
1 row in set (0.00 sec)
mysql> show create table t_tab7\G
*************************** 1. row ***************************
Table: t_tab7
Create Table: CREATE TABLE `t_tab7` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`own_domain_id` int(11) DEFAULT NULL,
`url` varchar(2000) NOT NULL,
`create_date` datetime DEFAULT NULL,
`friendly_name` varchar(255) DEFAULT NULL,
`section_name_id` int(11) DEFAULT NULL,
`type` int(11) DEFAULT NULL,
`status` int(11) DEFAULT NULL,
`week_entrances` int(11) DEFAULT NULL,
`week_bounces` int(11) DEFAULT NULL,
`canonical_url_id` int(11) DEFAULT NULL,
KEY `id` (`id`),
KEY `urlindex` (`url`(255)),
KEY `own_domain_id_type_status` (`own_domain_id`,`type`,`status`),
KEY `canonical_url_id` (`canonical_url_id`),
KEY `type` (`type`,`status`)
) ENGINE=InnoDB AUTO_INCREMENT=237034388 DEFAULT CHARSET=utf8
/*!50100 PARTITION BY RANGE (`type`)
(PARTITION p0 VALUES LESS THAN (0) ENGINE = InnoDB,
PARTITION p1 VALUES LESS THAN (1) ENGINE = InnoDB,
PARTITION p2 VALUES LESS THAN (2) ENGINE = InnoDB,
PARTITION pEOW VALUES LESS THAN MAXVALUE ENGINE = InnoDB) */
1 row in set (0.01 sec)
答案 0 :(得分：2)
尝试以下
select count(*)
from (Select id,create_tab3_id from tab6 where domain_id = 522) as tab1
left join tab6_element_tab2 tab2
on tab2.tab1nt_id = tab1.id
left join t_tab3 tab3
on tab1.create_tab3_id = tab3.id
left join t_tab4 tab4
on tab2.element_id = tab4.id and tab2.element_type_id = 1
left join t_tab7 tab5
on tab2.element_id = tab5.id and tab2.element_type_id = 2
如果您仅使用计数，则删除左连接t_tab3 tab3，如果可能，请添加域类型检查where子句
答案 1 :(得分：0)
在条件中使用的列上定义索引：
create index t_tab6_domain_id_index on t_tab6(domain_id);
查询本身似乎很好。